1. Field of the Invention
The present invention relates to an interior door lock assembly with a safety device to improve security.
2. Description of the Related Art
FIG. 5 of the drawings illustrates a typical door lock assembly which includes an exterior lock assembly 41 mounted to an outer side of a door plate (not labeled), an interior lock assembly, and a latch bolt assembly 43. The exterior lock assembly 41 includes a lock core (not labeled) with a tail piece 411, and a casing 42 is mounted around the exterior lock assembly 41 and constitutes a part thereof. The latch bolt assembly 43 includes a linking plate 431 having a rotating wheel 432 mounted therein through which the tail piece 411 is extended to rotate therewith for moving a latch bolt 433 upon rotation of the tail piece 411. The interior lock assembly includes a casing 44 secured to an inner side of the door plate by means of extending screws 443 through holes 441 defined in the casing 44. A switch button 45 includes a stub 451 formed on a side thereof and extended through a central hole 442 defined in the casing 44. The stud 451 includes a groove 452 defined therein for engaging with the tail piece 411 (a C-clip 453 is used to retain the tail piece 411 in position) to rotate therewith. In use, when a proper key is inserted into a keyway of the lock core from outside, the door lock can be unlatched under rotation of the key. The door lock assembly can also be unlatched from inside under rotation of the switch button 45. In some cases a chain lock 5 is provided to prevent the door from being opened from outside. Installation and use of the chain lock 5 is inconvenient. The present invention is intended to provide an improved interior door lock assembly to achieve the purpose of preventing the door from being opened from outside without the use of the chain lock.